The present invention relates to Al--Mg--Sc alloy compositions for use in aerospace applications, and the like, in which zinc, copper and other elements are added to the alloys to improve their tensile properties.
Aluminum alloys containing magnesium as the principal alloying element have two potential advantages for aircraft structures: they are lighter than the standard 2000 and 7000 series alloys; and unlike the latter materials, they are weldable by conventional fusion techniques, which could lower manufacturing costs by reducing the 2-3 million rivets typically used to assemble a commercial airliner.
A number of aluminum alloys have been developed in which magnesium is added to aluminum to improve strength. However, these alloys are not particularly suited for aerospace applications because their strength levels are not high enough. To address this problem, improved Al--Mg based alloys have been developed in which a dispersoid generating element, such as scandium, is added to the alloy. The addition of scandium to the alloys results in the formation of Al.sub.3 Sc dispersoids, which are intended to prevent recrystallization during thermomechanical processing, thereby imparting significantly greater strength to products made from the alloys. However, the tensile properties of Al--Mg--Sc based alloys deteriorate rapidly with thermomechanical processing and high temperature operations, such as hot rolling, that are necessary to manufacture aircraft fuselage sheet and other components. The degradation in tensile properties occurs because the scandium dispersoids must be small in size and large in number to impart increased strength to the alloy; presumably high temperature manufacturing operations cause them to grow too large to be effective recrystallization inhibitors.
One known solution to this problem is to add zirconium to the Al--Mg--Sc alloys. Zirconium acts to stabilize the dispersoids so that they can maintain their strength enhancing characteristics, even after the alloys have been subjected to high temperature operations. Although Al--Mg--Sc--Zr based alloys are thus somewhat suitable for aerospace applications, a need still remains for aluminum alloys that are even stronger than presently available alloys.